1. Field of the Invention
The present invention relates to a high frequency magnetic material ceramic composition for constituting a high frequency irreversible circuit component such as a circulator, an isolator or the like, and to an irreversible circuit component using the same.
2. Description of the Related Art
The size of radio communication devices in the communication apparatus field recently have been decreased, and the service frequency band-widths have been increased. Accordingly, it has been also required to reduce the size and increase the service band-widths for circuit parts intended for use in these fields.
Regarding the reduction in size of electronic parts, monolithic ceramic electronic parts employing laminated structures are known. The monolithic ceramic electronic part is ordinarily produced by preparing a plurality of formed ceramic green sheets and internal conductors, laminating the ceramic green sheets and the internal conductors, and firing the obtained laminate. In this method, the ceramic green sheets are fired simultaneously with the internal conductors. Therefore, it is necessary that a ceramic material for use in the ceramic green sheets can be sintered at a temperature lower than the melting point of the internal electrodes.
Yttrium (Y)xe2x80x94iron (Fe)xe2x80x94garnet materials used as one of the high frequency magnetic materials in circulators and isolators, which are typical high frequency circuit components, are widely known in the literature. See, e.g., Carl E. Patton xe2x80x9cEffective Linewidth due to Porosity and Anisotropy in Polycrystalline Yttrium Iron Garnet and Ca-V-Substituted Yttrium Iron Garnet at 10 GHzxe2x80x9d, Phys. Rev., vol. 179, No. 2 (1969). These materials are expressed by the chemical formula (Ca, Y)3(Fe, V)5O12.
The firing temperatures of the Yxe2x80x94Fe-garnet high frequency magnetic materials are high, that is, 1300xc2x0 C. or higher. Thus, Japanese Unexamined Patent Application Publication No. 6-61708 proposes that in order to allow sintering integrally with the internal conductors, Pd and Pt having a high melting point be used as the internal conductors.
Pd and Pt, which have high melting points of 1300xc2x0 C. or higher, can be sintered integrally with almost of all the high frequency magnetic materials. However, their resistivities are high. Thus, Pd and Pt have faults in that when they are used in laminated isolator components, the insertion loss is large.
It has been proposed that for the purpose of integrally firing the high frequency magnetic material and internal conductors, Ag and a material containing Ag as a major component be used to form the internal conductors, as described in Japanese Unexamined Patent Application Publication No. 7-212106.
When Ag, which has a low melting point of 961xc2x0 C., is used as an internal conductor, high frequency magnetic materials capable of being sintered at a temperature lower than the melting point of the internal Ag conductor are preferably employed. As high frequency magnetic materials capable of being sintered at a temperature of up to 1000xc2x0 C., a material having Bi added thereto and a garnet material having glass added thereto are exemplified. However, it has been difficult to produce these materials having a low loss, since heterogeneous phases are formed, and so forth.
Ca-V garnet materials for use as high frequency magnetic materials need to be sintered at a temperature of 1300xc2x0 C. or higher in order to obtain a dense structure sintered member. If the sintering temperature is lower than 1300xc2x0 C., a sufficient sintering density cannot be realized and the sintered member has problems in that the ferromagnetic resonance half-width (xcex94H) is small and the porosity is high.
It is known that the substitution by Bi and the addition of glass are effective for sintering at a low temperature. However, these components, Bi and glass, have faults in that they tend to generate heterogeneous phases so that the ferromagnetic resonance half-widths are increased.
It is an object of the present invention to provide a high frequency magnetic material ceramic composition useful as a high frequency magnetic material, which can be densely sintered at a low temperature with no heterogeneous phases being generated, and which has a small ferromagnetic resonance half-width, and to provide an irreversible circuit component using the same.
Accordingly, the present invention provides a high frequency magnetic material ceramic composition which comprises materials having the general formula (Ca, A)zCuxB8-x-zO12 in which A represents Y and/or at least one element selected from the rare earth elements excluding Y, B represents metal elements which are different from A and include at least Fe and V, x is a value of 0.002 less than x less than 0.2, z is a value of 3.0 less than zxe2x89xa63.09, and the Ca/V ratio is a value of 2.0 less than Ca/Vxe2x89xa62.4. The elements are, other than as just indicated, conventional in yttrium-iron-garnets.
The reason for the above-described limitations with respect to the formula is as follows. If the Ca/V ratio is stoichiometric (2.0) or lower, the sintering temperature is inconveniently 1360xc2x0 C., and if the Ca/V ratio is larger than 2.4, a heterogeneous phase is generated so that the ferromagnetic resonance half-width is increased.
When the amount of Cu, x, is xe2x89xa60.002, the low temperature sintering effect can not be obtained because the sintering temperature becomes 1100xc2x0 C. or higher. If xxe2x89xa70.2, a heterogeneous phase is generated, and undesirably, the ferromagnetic resonance half-width is increased.
To obtain a high frequency magnetic material which can be sintered at a temperature of less than 1100xc2x0 C. and has a small ferromagnetic resonance half-width, the range of 2.0 less than Ca/Vxe2x89xa62.4 and 0.002 less than x less than 0.2 in the above-described general formula is preferred. Preferably, the range of x is 0.005xe2x89xa6xxe2x89xa60.1. Regarding the Cu amount, the low temperature sintering effect is remarkable at 0.02xe2x89xa6xxe2x89xa60.1.
Examples carried out at z=3.01 are described in this specification. Desirably, z is in the range of 3 (stoichiometric value) to 3.09. In this range, the low temperature sintering effect caused by Cu can be achieved.
In the high frequency magnetic material ceramic composition, B preferably further includes at least one element selected from Al, In and Zr. In the above-described constitution, the ferromagnetic resonance half-width can be set to be still smaller, since at least one of Al, In and Zn is further included in B.
The present invention moreover provides an irreversible circuit component which comprises a ferrite member made of the above-described high frequency magnetic material ceramic composition, plural center electrodes arranged in the ferrite member in such a manner as to be electrically insulated from each other and intersect, and a magnet section for applying a DC magnetic field to the respective center conductors and the ferrite member.
The firing temperature of the high frequency magnetic material ceramic composition is low, and the ferromagnetic resonance half-width is small. Thus, the heating cost can be reduced, and scattering and evaporation of a metallic part can be reduced, so that the circuit component has a high accuracy. Moreover, the loss, especially the loss at a high frequency, can be reduced due to the small ferromagnetic resonance half-width. With the irreversible circuit component of the present invention, superior characteristics such as reduction of cost, high accuracy and low loss can be achieved.